DESCRIPTION Lamin, a nuclear intermediate filament, forms a mesh of fibers underlying the nuclear envelope. There is evidence that lamins and lamin associated proteins anchor nuclear pores, provide attachment sites for chromosomes and play a role in reassembly of the nucleus after mitosis. Lamin mutations have many effects, including sterility and neural damage. This suggests that the long term goal of this research, knowing more about the functional interaction between components of the nuclear periphery and chromatin, might contribute to an understanding of disease. Mosaic analysis of a putative null mutation in Dm0, the Drosophila type B lamin, will be used to determine the role of Dm0 in properly distributing nuclear pores on the nuclear envelope and in the organization of chromatin. It will be determined in malin C, the other Drosophila lamin, mitigates the effect of a reduction in Dm0. Alterations in nuclear structure that occur in clonal patches of lamin-deficient cells will be characterized and quantitated using new techniques in high resolution 3D wide-field fluorescence microscopy. The order in which lamin Dm0, nuclear core glycoproteins, and lamin C attachment to chromatin and/or enter the nucleus after mitosis will be determined by live analysis in the early embryo. Techniques for visualizing specific loci on the Drosophila chromosomes in real time will allow the dynamics of nuclear envelope association of chromatin to be determined. Using the tools developed for this research it will be possible to continue the investigation by doing mutational analysis of lamin in somatic clones and live analysis of the dynamics of other proteins of the nuclear periphery.